“There are a lot of security issues in the design of the iPhone that lend themselves to retaining more personal information than any other device,” said Jonathan Zdziarski, a former computer hacker who now teaches US law enforcers how to retrieve data from mobile phones.

“These devices organise people’s lives and, if you’re doing something criminal, something about it is going to go through that phone.” Apple has sold more than 50 million iPhones since the product was launched in 2007.

Mr Zdziarski told The Daily Telegraph he suspected that security had been neglected on the iPhone as it had been intended as a consumer product rather than a business one like rivals such as the Blackberry.

An example was the iPhone’s keyboard logging cache, which was designed to correct spelling but meant that an expert could retrieve anything typed on the keyboard over the past three to 12 months, he said.

In addition, every time an iPhone’s internal mapping system is closed down, the device snaps a screenshot of the phone’s last position and stores it.

Investigators could access “several hundred” such images from the iPhone and so establish its user’s whereabouts at certain times, he said.

In a further design feature that can also help detectives, iPhone photos include so-called “geotags” so that, if posted online, they indicate precisely where a picture was taken and the serial number of the phone that took it.

“Very, very few people have any idea how to actually remove data from their phone,” Sam Brothers, a mobile phone researcher for US Customs and Border Protection told the Detroit Free Press.

“It may look like everything’s gone but for anybody who’s got a clue, retrieving that information is easy.”